As some readers may know, I am no longer living in Berlin. Before I lose track of my thoughts, there's one more Berlin topic I want to tackle: graffiti.

To say that Berlin is covered in graffiti is merely to state the obvious.

Close your eyes and imagine Germany, and visions of beer steins and BMWs probably dance in your head. And you imagine a well-run place. Ordentlichkeit (order, orderliness) is a national virtue, right? So why is the capital city covered in spray paint and stickers--strong evidence of the absence rather than the presence of Ordentlichkeit?

In another city in another country, graffiti would be a sign of urban blight. In Berlin, it's art.

Where there's art, there are art books. Urban Illustration Berlin is essentially a museum catalog, except that the art is all over the city, and may have been painted over by the time you get there. Click here to peek inside the book.

E. and I purchased, as art, a photo of graffiti by an artist known as xoxo. We paid money so we can look at graffiti whenever we want.

What explains the Berlin's love affair with graffiti?

My first hypothesis has to do with history. The Berlin Wall was an endless canvas, an eyesore, and a reminder of the German fissure. The solution? Paint it. Hide it.

That's the great Bruno Ganz walking along the Berlin Wall. See the graffiti in the background? I don't know the whole story but 1) I believe it was commissioned for the film 2) it's definitely by a particular artist 3) any Berliner would recognize it. It's famous. It's art.

This hypothesis will only take you so far, however. The West Berlin side of the wall was covered in graffiti, but my understanding is that the East German authorities kept their side of the wall clean. These days if anything graffiti is more evident in the former east, whereas the west is a bit cleaner.

My second hypothesis is more abstract, but it strikes me as the best explanation. In the absence of graffiti, the "meaning" of a wall is whatever its owner choses. A shiny coat of white paint on your Gründerzeit home tells the world you have money and a well-engineered car. An abraded wall of crumbling stucco and leftover war damage tells another story. And so does a wall that's been tagged, stenciled, and illustrated.

The historical narrative of Berlin is still up for grabs. Is it a Prussian city? A Nazi city? An East German city? A world capital? A squat? A yuppie paradise? No one is sure, but everyone has ideas. Each new graffito is a fresh assertion: This, not that, is what this wall is about. This, not that, is what Berlin is. And until there's consensus on a narrative, no blank wall is safe.